Strand materials such as textile yarns, filaments and the like frequently are guided or transported along predetermined paths of travel by entrainment of the strand materials about at least portions of circumferential strand receiving grooves of sheaves or pulleys. In certain strand handling operations, such pulleys or sheaves are driven or braked in order to control movement of or tension in the strand material while in other strand handling applications the rotation of such a sheave or pulley is used to measure lengths of strand material or rates of movement of strand material. Examples of such operations may be found in White U.S. Pat. No. 3,797,775 and White et al U.S. Pat. No. 3,858,416.
As will be appreciated, slippage of a strand material relative to an engaged sheave or pulley may present no difficulty where the only function for the sheave or pulley is to guide strand material along a desired path of travel. However, slippage can introduce significant inaccuracies in circumstances where strand material tension is being controlled or some characteristic of strand movement is being controlled or measured.
It has been proposed heretofore that the coordination of sheave rotation with strand movement may be improved by more positively gripping a strand which engages a sheave. In certain prior structures designed for such a purpose, an annular member or ring defining a circumferential groove has been mounted on a central hub which is affixed, by suitable means to a central shaft. While such arrangements have achieved some success, difficulty has on occasion been encountered due to high rates of change of rotational speeds such as occur on rapid acceleration or braking of strand movement. Relatively high torques arising under such circumstances may cause slippage of the elastomeric ring member relative to the hub, leading to loss of control and inaccuracy in measurements.